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Worn valve tips , valve action geometry and Mushroom head adjusters.

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After a lifetime (or two)  of use the 1960  99 is making a few unexplained noises. I  will be investigating soon . In the meantime i have been gifted a set of Mushroom head adjusters (ta mate).  I know the valve tips are indented and the valves are from 1959 when the bike was built. So its likely that new ones are in order. Compression is still very good and  this 80 year old would be happy with less..  We know that the AMC factory  lengthened the valves and shorten pushrods to correct a long standing error in valve geometry on heavy twins  ,but they did not make it clear when the error was instigated. I had  assumed that only the DD head was affected , but thats an assumption only.  If the action can be improved on the 99 .why not?. I will be fitting a compression plate to assist easy starting and that will effectively shorten the pushrods , the valves will probably have effectively lengthened themselves with grinding in sessions and seat errosion  so its possibly corrected itself !.  This was the situation on our Atlas. The 99 has always been unexpectedly quick according to other members.  Anyway i can lengthen valves with RGM lashcaps and grind off indentation on old valves if happy with the condition . All that i need is a practical  routine to evaluate the valve /rocker action .  Suggestions welcomed.

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Measuring rocker action is very painstaking. You have to use a dial gauge and measure the full lift of the valve. Then you have to find the halfway point, then judge if the valve is at 90deg to the rocker!! Simple-NOT HUH! I have monitored our Forum with regarding the Commando problems with valves and geometry and nobody seems to fully understand or has measured it. I have done this on a Reliant engine-got it wrong-decided that Reliant got it right!

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It's not easy to get a clear side view with the Dommie head design.  But one thing to help must be to swap out all the springs for some much lighter ones (like Amal carb springs).  Then it will be much easier to watch (and perhaps take pictures, with a degree disc fitted) to see and record all the movements without the cam kicking it past the watch points.  An other issue is - should it fit best half way up the cam movement, or towards the peak of the cam where the forces must be biggest?  

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Thanks Alan and Dave, there has been the odd article in Roadholder about valve gear action . i have not been able to get the search facility to work. There are some ex racers out there who may chime in, hopefully. Can we still get Silchrome stem valves ?  ,they seem to work best with cast iron guides. 

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............the whole point of maximum efficiency of your valve gear on ALL 4 stroke engines is that at half lift the rocker and valve need to be at right angles to each other. This not an issue of where you are on the cam. Also David I would not think you have to do all the rockers/valves once you have measured one then we must assume you have the same rocker advantage and valve length in your head. Then of course if you have a higher lift cam the 90Deg point will change again!!
This is effected by so many things-the length of the valve stem the length of the push rods, which in turn are affected by the cam followers which in turn are held in the barrel’s. Then there is the head height/barrel. It seems  that Norton's in their wisdom over the years changed several of these points without full thought of ALL the points, hence the rocker/valve action was compromised (messed up), then another factor ie valve length would be changed, and then of course the wrong valve would be put in with another set of push rods, then the compression was upped by lowering the head so certainly on the Commando we had a mobile disaster. And I do not know if anyone has managed to measure the result, which of course would only be effective on the engine it is measured on.
Nest of worms is a perfect description.

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Both inlets will be the same - and both exhausts - so only need to do one of each...

Could you mark (with fine paint pen or  bow pen) across the rocker boss to the head, at each end of the rocker movement?  Then move to the half way point and inspect to see if the tappet is either in line (correct) or out of line (incorrect)?

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I have just realised that a 650 motor I am working on has a heavilly skimmed head and will probably need the pushrods to be shorter .   Perhaps i was better off  in blissfull ignorance!.

 



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